During generation and use of steam, it is often desirable to know the quality of the steam. Various techniques have evolved for measuring steam quality. The more common of these techniques involve using various colorimeters and orifice meters. Other techniques are available utilizing properties of feed water compared to the properties of the liquid phase of the steam. A discussion of these techniques is given in U.S. Pat. No. 3,596,516, issued Aug. 3, 1971. There have also been proposals to determine steam quality using captured samples of the steam water mixture. None of the techniques of determining steam quality, however, has been entirely satisfactory for field use. There is, therefore, still need for a method and apparatus for readily determining the quality of steam flowing in a steam line.
Heretofore, William G. Steltz, in an article titled "The Critical and Two-Phase Flow of Steam" in the Journal of Engineering Power of April, 1961, related a critical pressure ratio of P.sub.exhaust /P.sub.inlet to inlet enthalpy in computer studies. Steltz, however, made several assumptions which are not applicable to actual field determination of the quality of wet steam flowing in a steam line. Other articles of background interest related to two-phase flow include: "Critical Two-Phase, Steam-Water Flows," by H. Fauske, from Proceedings of the 1961 Heat Transfer and Fluid Mechanics Institute; "Steam-Water Critical Flow Through Pipes," by Russell James, from the Institution of Mechanical Engineers, Vol. 176, No. 26, 1962; "Some Improved Steam Property Calculation Procedures," by R. B. McClintock and G. J. Silvestri, from the Journal of Engineering for Power, April, 1970; "Metering of Steam-Water Two-Phase Flow by Sharp-Edged Orifices," by Russell James, from the Institution of Mechanical Engineers, Vol. 180, Pt. 1, No. 23, 1965-66.